Polishing Preps and Bond Strengths, Is there a Connection?

I am routinely asked when I teach bonding and cementation or preparation design about polishing. The question is always some form of should we or shouldn’t we polish? Does it have a negative effect on bond strengths? Does it improve clinical success and is therefore worth the additional time?

These are all valid questions.  The concept of polishing preps is a relatively new one for me and began about 9 years ago. The genesis was at a lecture where the presenter showed slides of polishing his preps.  I went home curious enough about it to ask my laboratory technician. His response was very simple, “ I love when my doctors polish their preps.” When I asked why he explained the smoothness of the die made fabricating a well fitting restorations easier. Polished preps normally come hand in hand with smooth margins, which make sealing the margins easier on his end. All of these things sounded to me like improved clinical results, which would translate to improved longevity for my patients. When I began using digital impressions, it was immediately obvious to me how much the smoothness of the prep improved my image and the final result.

Bond strength is really a way of asking about retention. If you are cementing a restoration, retention has got to come from your preparation design having adequate retention and resistance form. The cement is simply a “luting” agent to fill the micro gap between the restorative material and the tooth. The addition of surface roughness does not improve retention significantly enough to alter prep design and replace these basic principles. When we are bonding a restoration with resin cement, and depending on adhesion for chemical versus mechanical retention does it matter? The chemical adhesion and bond strength comes from the proper formation of a hybrid zone with dentin and enamel bond. There is an expanding body of research that shows the addition of surface roughness does not improve or increase bond strengths. Additionally, some of the studies are showing that the use of coarser burs and the thicker smear layer created can make getting adequate bond strengths more difficult.

Given the lack of value from roughness and the benefit in impression accuracy (digital or physical) and restoration fabrication from smooth preps I follow a protocol for polishing. My initial polish is completed with a fine ( red Stripe) diamond. After this I reshape a white stone to match my margin design it is the final phase of the polishing process prior to final impressions.